Non-destructive testing and assessment of a piping system with excessive vibration and recurrence crack issue: An industrial case study

Flow in piping generates random excitation which is non-periodic and that means resonance will not be the key factor to pipe failure. One of the main causes of pipe failure is weak supports. Due to their dissimilar stiffness in the piping system, it leads to low frequency and high amplitude flow induced vibration that causes high cyclic stress resulting in high cycle fatigue failure of the joints. Other contributing factors in pipe failure are poor or inadequate design, poor workmanship during installations or maintenance and inadequate or weak and flexible support. These pipes are usually required to work non-stop for 24 hours a day 7 days a week for weeks, months or years at a time. Regular monitoring and in-service dynamic analysis should ensure continuous and safe operation. This paper presents a case study on monitoring, diagnosis, and maintenance of a piping system. High vibration was observed during routine maintenance, in a 30 m high, 24 inch diameter amine pipes at an oil and gas processing plant in southern Thailand. Amine liquid leakage due to high cycle fatigue crack was reported at the piping bearing and this remained a major concern for the personnel at the plant. A non-destructive testing approach which relies on a combined experimental techniques (i.e. Operating Deflection Shapes (ODS)) and computational mechanics (i.e. Finite Element (FE) modal analysis, Computational Fluid Dynamics (CFD) Analysis, Fluid-Structure Interaction (FSI) Analysis) was used to assess the structural integrity of the piping and in the effort of proposing a suitable recommendation in rectifying the high vibration issue. The analyses concluded that the root cause of high vibration was due to inadequate and weak piping support. As a result, additional supports were proposed to counter the deflection of the piping generated by the flow. The supports were found effective in reducing vibration in which the stress concentration at the new supports and the piping was considered relatively low

Enhancement of Impact-Synchronous Modal analysis (ISMA) with number of averages.

A new method, namely Impact-synchronous Modal Analysis (ISMA), utilizing the modal extraction technique commonly used in Experimental Modal Analysis performed in the presence of the ambient forces, is proposed. In ISMA, the extraction is performed while the machine is running, utilized Impact-synchronous Time Averaging prior to performing the Fast Fourier Transform. The number of averages had a very important effect when applying ISMA on structures with dominant periodic responses of cyclic loads and ambient excitation. With a sufficient number of impacts, all the unaccounted forces were diminished, leaving only the response due to the impacts. This study demonstrated the effectiveness of averages taken in the determination of dynamic characteristics of a machine while in different rotating speeds. At low operating speeds that coincided with the lower natural modes, ISMA with a high number of impacts determined the dynamic characteristics of the system successfully. Meanwhile, at operating speeds that were away from any natural modes, ISMA with a moderate number of averages taken was sufficient to extract the modal parameters. Finally for high-speed machines, ISMA with a high number of impacts taken has limitations in extracting natural modes close to the operating speed

Feasibility study of performing experimental modal analysis with oblique impact testing using various oblique impact directions

© 2020 Faculty of Engineering, Alexandria University Oblique impact excitation has been introduced in Experimental Modal Analysis (EMA), with the great advantage of reducing the conventional EMA's testing time by a factor of three. One major constraint of this technique is the investigation of the effect of various oblique impact directions towards its accuracy in determining the structural dynamic characteristic. This feasibility study is difficult to be achieved in practice, as it involves a lengthy amount of experimental works using various oblique impact directions. To solve this problem, a mathematical model has been developed to synthesize the FRF due to oblique impact (i.e. oblique FRF) in this study. The synthesized oblique FRFs show great agreement with the measured oblique FRFs in various oblique impact directions, which validate the reliability of the usage of the proposed synthesis method. The performance of the oblique impact testings using various impact angles is investigated. The results show that the oblique impact testing has a high success rate to extract directional modes in many impact directions, however wrong selection of the impact direction will lead to mode estimation failure. Good selection of impact direction based on force and modal strengths are demonstrated to ensure an accurate estimation of the structural dynamic characteristics

Energy Harvesting Based on a Novel Piezoelectric 0.7PbZn0.3Ti0.7O3-0.3Na2TiO3 Nanogenerator

Recently, piezoelectric materials have achieved remarkable attention for charging wireless sensor nodes. Among piezoelectric materials, non-ferroelectric materials are more cost effective because they can be prepared without a polarization process. In this study, a non-ferroelectric nanogenerator was manufactured from 0.7PbZn0.3Ti0.7O3-0.3Na2TiO3 (PZnT-NT). It was demonstrated that the increment of conductivity via adding the Na2TiO3 plays an essential role in increasing the permittivity of the non-ferroelectric nanogenerator and hence improved the generated power density. The dielectric measurements of this material demonstrated high conductivity that quenched the polarization phase. The performance of the device was studied experimentally over a cantilever test rig; the vibrating cantilever (0.4 ms-2) was excited by a motor operated at 30 Hz. The generated power successfully illuminated a light emitting diode (LED). The PZnT-NT nanogenerator produced a volume power density of 0.10 μw/mm3 and a surface power density of 10 μw/cm2. The performance of the proposed device with a size of (20 × 15 × 1 mm3) was higher in terms of power output than that of the commercial microfiber composite (MFC) (80 × 57 × 0.335 mm3) and piezoelectric bimorph device (70 × 50 × 0.7 mm3). Compared to other existing ferroelectric and non-ferroelectric nanogenerators, the proposed device demonstrated great performance in harvesting the energy at low acceleration and in a low frequency environment

Non-destructive testing and assessment of dynamic incompatibility between third-party piping and drain valve systems: An industrial case study

This paper presents the outcome of an industrial case study that involved condition monitoring of piping system that showed signs of excess fatigue due to flow-induced vibration. Due to operational requirements, a novel non-destructive assessment stratagem was adopted using different vibration analysis techniques - such as experimental modal analysis and operating deflection shapes - and complemented by visual inspection. Modal analysis carried out near a drain valve showed a dynamic weakness problem (several high-frequency flow-induced vibration frequency peaks), hence condition-based monitoring was used. This could easily be linked to design problem associated with the dynamic incompatibility due to dissimilar stiffness between two third-party supplied pipe and valve systems. It was concluded that this is the main cause for these problem types especially when systems are supplied by third parties, but assembled locally, a major cause of dynamic incompatibility. It is the local assembler's responsibility to develop skills and expertise needed to sustain the operation of these plants. This paper shows the technique used as result of one such initiative. Since high amplitude, low-frequency displacement can cause low cycle fatigue, attention must be paid to ensure flow remains as steady state as possible. The ability to assess the level of design incompatibility and the level of modification required using non-destructive testing is vital if these systems are to work continuously. © 2014 Taylor & Francis

Development and Validation of Experimental Modal Analysis with Fixture-Free Oblique Impact Testing Based on Vector Projection Method

Experimental modal analysis (EMA) with oblique excitation (i.e. oblique impact testing) is useful in improving the long testing time problem of conventional EMA with normal excitation (i.e. tri-axial normal impact testing), in order to extract all important dynamic characteristics of a 3D complex structure. In this study, a new methodology involving vector projection method is introduced to find the driving point frequency response function (FRF) in the oblique direction, without the need of special fixture with oblique-oriented impedance head. Hence, it presents a low cost and practical solution to scale the mode shape, as compared to the traditional approach. Moreover, the concurrent forces characteristic of the oblique excitation is used in the development of the theoretical relationship between the FRF with oblique excitation and normal excitation. This is important for the validation of the oblique impact testing result, such as the FRF and modal parameter estimations. Experimental results show that the oblique impact testing has reliable and effective results, as compared with the tri-axial normal impact testing in terms of the FRF correlation, natural frequency discrepancy, modal damping ratio error and modal assurance criterion (MAC) of the unit modal mass (UMM) mode shape

Impact force identification with pseudo-inverse method on a lightweight structure for under-determined, even-determined and over-determined cases

Force identification using inverse technique is important especially when direct measurement through force transducer is not possible. Considering the effects of impact excitation force on the integrity of a lightweight structure, impact force identification has become the subject of several studies. A methodology utilising Operating Deflection Shape (ODS) analysis, Frequency Response Function (FRF) measurement and pseudo-inverse method to evaluate the dynamic force is presented. A rectangular plate with four ground supports was used as a test rig to simulate the motions of a simple vehicle body. By using the measured responses at remote points that are away from impact locations and measured FRFs of the test rig, unknown force locations and their time histories can be recovered by the proposed method. The performance of this approach in various cases such as under-determined, even-determined and over-determined cases was experimentally demonstrated. Good and bad combinations of response locations were selected based on the condition number of FRF matrix. This force identification method was examined under different response combinations and various numbers of response locations. It shows that in the over-determined case, good combination of response locations (i.e. low average of condition number of FRF matrix) and high number of response locations give the best accuracy of force identification result compared to under-determined and even-determined cases

A modified tabu search algorithm for cost-based job shop problem

10.1057/jors.2009.9Journal of the Operational Research Society614611-619JORS

An application of tabu search algorithm on cost-based job shop problem with multiple objectives

10.1109/IEEM.2007.4419324IEEM 2007: 2007 IEEE International Conference on Industrial Engineering and Engineering Management912-91

A comparative study of vibrational response based impact force localization and quantification using radial basis function network and multilayer perceptron

Impact force identification from response sensors is important especially when force measurement using force sensor is not possible due to the installation or dynamic characteristic altering problems. For example, the bump-excited impact force acting on vehicle wheel or ship collision on an offshore structure. Among various existing impact identification approaches, neural network based force identification method has received great attention because one does not need to have a system model. Thus, it is less likely to be affected by ill-posed problem that often occurs during the inversion process. So far, previous studies focused on solving the impact force identification problem using only the conventional Multilayer Perceptron (MLP). Thus, there is a room for improvement to find an alternate algorithm that has great advantage over MLP. For this reason, this study proposes Radial Basis Function Network (RBFN) for possible further improvement in impact identification task. A comparative study between these two algorithms was conducted via experimental approach. Impact forces were made on a Perspex plate structure which was designed to produce similar dynamic behavior of a typical vehicle. Impact locations were fixed at four edges of the test rig to simulate impact events at a vehicle's wheels. Time-domain peak-to-peak and peak arrival time features were extracted from accelerometer data to use as network inputs. Few training data were taken in the way that they represent the entire range of magnitudes of all trial impacts made throughout the experiment. In overall, RBFN improved the impact localization and quantification accuracies by decreasing 32.98% and 40.91% error respectively compared to MLP. The improvement was mainly due to the RBFN's strong approximation ability and its superior tolerance to experimental noises/uncertainties